There is known from patent document EP 0 448 018 a compass- watch comprising an electronic horological movement, two magnetic sensors serving to sense directly the terrestrial magn-etic flux, a unit for processing signals furnished by the two magnetic sensors in order to determine the magnetic azimuth of a reference axis of the watch, electronic means for management and control serving to drive display means to a geographic direction and in particular the direction of the geographic north. In order to accomplish this, it is provided that the magnetic declination of the locality where the watch user is located can be furnished through the electronic management and control means in a manner whereby such electronic means can determine the geographic azimuth corresponding to the measured magnetic azimuth.
The prime function of an arrangement having a compass function is to indicate as correctly as possible the direction of the geographic north or of any geographic azimuth whatsoever. In order to accomplish this, in addition to knowing the magnetic declination of the locality of utilization, it is above all necessary, that the means for detecting the direction of the magnetic north be precise and reliable.
The patent document EP 0 448 018 proposes to determine the direction of the magnetic north by using two magnetic sensors, each formed by a magnetic resistance. Such sensors are sensitive to the flux of the terrestrial magnetic field along a preferred direction. Thus, each of the two sensors measures substantially the component of the terrestrial magnetic flux in the region in which such sensor is located, according to the preferred direction. The two sensors are arranged in a manner such that their respective preferred directions are orthogonal. The information received by the two sensors enables the determination of a direction, such direction being interpreted by the electronic management and control means as being the direction of the magnetic north.
The determination of the direction of the magnetic north proposed in the above-mentioned document is delicate and not very reliable. Initially, the direction of the magnetic north, measured with the help of the two magnetic sensors, is dependent on the orientation of the plane defined by the two preferred directions of the two sensors. If the watch user does not maintain the general plane of the watch horizontal, the measure of the direction of the magnetic north is distorted.
Secondly, the terrestrial magnetic field is disturbed by the environment of the magnetic sensors and in particular by the magnetic masses of the electronic horological movement housed within the watch. Such magnetic masses locally deform the terrestrial magnetic flux lines to the extent that the respect-ive components of the terrestrial magnetic flux sensed by the two magnetic sensors do not enable the exact determination of the direction of the terrestrial magnetic north.
Finally, it will be noted that the above-mentioned document gives no information as to the positioning of the two magnetic sensors within the compass watch or of the arrangement used as compass.
The purpose of the present invention is to overcome the above-mentioned drawbacks in furnishing a watch comprising an arrangement for indicating a given geographic direction exhibiting high precision in the determination of the magnetic north.